Electrical characterization of growth-induced defects in bulk-grown ZnO

We have investigated and compared the defects in ZnO grown by two methods, namely seeded chemical vapour transport (SCVT) and melt-growth (MG), using conventional deep level transient spectroscopy (DLTS) and high resolution (Laplace) DLTS with Au and Ru Schottky barrier diodes. Both materials contained two prominent defects, E1, at ECEC–0.12 eV and E3 at ECEC–0.29 eV. The SCVT ZnO has E1 as the main defect with a concentration of about 1016 cm−3, while the MG ZnO has E3 as the main defect with a concentration of above 1016 cm−3. It has been speculated that this defect is the oxygen vacancy in ZnO. High resolution Laplace DLTS suggests that this level could consist of two closely spaced levels but with different capture cross-sections. The relative concentrations of these defects were found to vary across the region probed by DLTS. The E1 and E3 defects also showed opposite trends in an electric field: an increase in electric field enhanced emission from E1 whereas it slowed down emission from E3. The peak splitting and field dependence may, however, be a consequence of a non-exponential transient. Finally, etching in HCl:H2O did not affect the defect concentrations or introduce additional defects in ZnO in the MG ZnO.